The present invention relates to switched capacitor amplifiers and applications therefor.
Switched capacitor amplifiers are known. Typically, they include one or more input branches each having an input capacitor selectively switched to an input voltage source and a reference voltage source. The branches may terminate at a second terminal of their respective input capacitors, which may be input to a first terminal of an operational amplifier (colloquially, “op amp”). An output capacitor may bridge between an output of the op amp and the first terminal thereof. A second terminal of the op amp may be tied to ground.
Operation of the traditional switched capacitor amplifier consumes two cycles of a driving clock signal. During the first cycle, the amplifier precharges and evaluates, generating a potential across the output capacitor. During the second cycle, the potential of the output capacitor is held at the amplifier output while another circuit element samples it.
The two-cycle operation of the switched capacitor amplifier is disadvantageous, particularly in pipestaged applications where a number of the switched capacitor amplifiers may be tied to one another in a cascaded relationship. If an input potential were applied to a first stage during a first cycle, an output would be available to the second stage in a second clock cycle. The first stage, however, could not accept a new input until the third clock cycle and could not generate a second output until the fourth clock cycle. This delay reduces throughput of an entire pipestaged system; it would be far better for a switched capacitor amplifier to generate an output in each and every clock cycle of operation.
While it would be possible to use existing architectures for switched capacitor amplifier to generate an output in each clock cycle, it would be necessary to increase the size and bulk of the components thereof, notably the op amp and output capacitor. Increased size and bulk of these components also would be disadvantageous. Larger components consume more power and are difficult (at least, expensive) to manufacture in integrated circuits. Accordingly, there is a need for a new architecture for switched capacitor amplifiers that can achieve increased throughput while permitting small component size.